How to Swap Two Elements in a LinkedList in Java?

Given a Linked List, the task is to swap two elements without disturbing their links. There are multiple ways to swap. Elements can be swapped using by swapping the elements inside the nodes, and by swapping the complete nodes. 

Example:

Input :- 10->11->12->13->14->15
         element1 = 11
         element2 = 14
         
Output :- 10->14->12->13->11->15

Method 1: Using the in-built set method

Swap the two elements in a Linked List using the Java.util.LinkedList.set() method. In order to achieve our desired output, first, make sure that both the elements provided to us are available in the Linked List. If either of the elements is absent, simply return. Use the set() method to set the element1’s position to element2’s and vice versa.

Below is the code for the above approach:

Java

// Swapping two elements in a Linked List in Java

import java.util.*;

class GFG {
    public static void main(String[] args)
    {

        LinkedList<Integer> ll = new LinkedList<>();

        // Adding elements to Linked List
        ll.add(10);
        ll.add(11);
        ll.add(12);
        ll.add(13);
        ll.add(14);
        ll.add(15);

        // Elements to swap
        int element1 = 11;
        int element2 = 14;

        System.out.println("Linked List Before Swapping :-");

        for (int i : ll) {
            System.out.print(i + " ");
        }

        // Swapping the elements
        swap(ll, element1, element2);
        System.out.println();
        System.out.println();

        System.out.println("Linked List After Swapping :-");

        for (int i : ll) {
            System.out.print(i + " ");
        }
    }

    // Swap Function
    public static void swap(LinkedList<Integer> list,
                            int ele1, int ele2)
    {

        // Getting the positions of the elements
        int index1 = list.indexOf(ele1);
        int index2 = list.indexOf(ele2);

        // Returning if the element is not present in the
        // LinkedList
        if (index1 == -1 || index2 == -1) {
            return;
        }

        // Swapping the elements
        list.set(index1, ele2);
        list.set(index2, ele1);
    }
}

Output

Linked List Before Swapping :-
10 11 12 13 14 15 

Linked List After Swapping :-
10 14 12 13 11 15

Time Complexity: O(N), where N is the length of Linked List

Method 2: Using our very own Linked List

Given a linked list, provided with two values, and swap nodes for two given nodes.

Below is the implementation of the above approach:

Java

// Java Program to Swap Two Elements in a LinkedList
class Node {
    int data;
    Node next;
    Node(int d)
    {
        data = d;
        next = null;
    }
}

class LinkedList {
    Node head; // head of list

    // Function to swap Nodes x and y in
    // linked list by changing links
    public void swapNodes(int x, int y)
    {
        // Nothing to do if x and y are same
        if (x == y)
            return;

        // Search for x (keep track of prevX and CurrX)
        Node prevX = null, currX = head;
        while (currX != null && currX.data != x) {
            prevX = currX;
            currX = currX.next;
        }

        // Search for y (keep track of prevY and currY)
        Node prevY = null, currY = head;
        while (currY != null && currY.data != y) {
            prevY = currY;
            currY = currY.next;
        }

        // If either x or y is not present, nothing to do
        if (currX == null || currY == null)
            return;

        // If x is not head of linked list
        if (prevX != null)
            prevX.next = currY;
        else // make y the new head
            head = currY;

        // If y is not head of linked list
        if (prevY != null)
            prevY.next = currX;
        else // make x the new head
            head = currX;

        // Swap next pointers
        Node temp = currX.next;
        currX.next = currY.next;
        currY.next = temp;
    }

    // Function to add Node at beginning of list.
    public void push(int new_data)
    {
        // 1. alloc the Node and put the data
        Node new_Node = new Node(new_data);

        // 2. Make next of new Node as head
        new_Node.next = head;

        // 3. Move the head to point to new Node
        head = new_Node;
    }

    // This function prints contents of linked
    // list starting from the given Node
    public void printList()
    {
        Node tNode = head;
        while (tNode != null) {
            System.out.print(tNode.data + " ");
            tNode = tNode.next;
        }
        System.out.println();
    }

    // Driver program to test above function
    public static void main(String[] args)
    {
        LinkedList llist = new LinkedList();

        // The constructed linked list is:
        // 1->2->3->4->5->6->7
        llist.push(7);
        llist.push(6);
        llist.push(5);
        llist.push(4);
        llist.push(3);
        llist.push(2);
        llist.push(1);

        System.out.println("Linked List Before Swapping :-");
        llist.printList();

        llist.swapNodes(4, 3);

        System.out.println("Linked List After Swapping :-");
        llist.printList();
    }
}

Output

Linked List Before Swapping :-
1 2 3 4 5 6 7 
Linked List After Swapping :-
1 2 4 3 5 6 7

Time Complexity: O(N), where N is the length of Linked List